Vaccination is the most important route of dealing with viral infections. Although a number of antiviral agents are available, typically these agents have limited efficacy. Administering antibodies against a virus may be a good way of dealing with viral infections once an individual is infected (passive immunization) and typically human or humanized antibodies do seem promising for dealing with a number of viral infections. But the most efficacious and safe way of dealing with virus infection is, and probably will be, prophylaxis through active immunizations. Active immunization is generally referred to as vaccination and vaccines comprising at least one antigenic determinant of a virus, preferably a number of different antigenic determinants of at least one virus, e.g., by incorporating in the vaccine at least one viral polypeptide or protein derived from a virus (subunit vaccines). Typically, the formats mentioned so far include adjuvants in order to enhance an immune response. This also is possible for vaccines based on whole virus, e.g., in an inactivated format. A further possibility is the use of live, but attenuated forms of the pathogenic virus. A further possibility is the use of wild-type virus, e.g., in cases where adult individuals are not in danger from infection, but infants are and may be protected through maternal antibodies and the like. Production of vaccines is not always an easy procedure. In some cases the production of viral material is on eggs, which leads to difficulty in purifying material and extensive safety measures against contamination, etc. Also production on bacteria and or yeasts, which sometimes, but not always, is an alternative for eggs, requires many purification and safety steps. Production on mammalian cells would be an alternative, but mammalian cells used so far all require, for instance, the presence of serum and/or adherence to a solid support for growth. In the first case, again, purification and safety and e.g., the requirement of protease to support the replication of some viruses becomes an issue. In the second case, high yields and ease of production become a further issue. The present invention overcomes at least a number of the problems encountered with the production systems for production of viruses and/or viral proteins for vaccine purposes of the systems of the prior art.